I. Field of the Invention
The present invention relates generally to variable geometry devices employed in turbine engines and, more particularly, to such a device for use in the nozzle passageway between the turbine engine combustion chamber and the turbine stage or stages.
II. Description of the Prior Art
A conventional turbine engine includes a support housing, a compressor having an outlet rotatably mounted within the support housing and a diffuser passageway which fluidly connects the compressor outlet to a combustion chamber also contained within the support housing. Following combustion within the combustion chamber, the exhaust gases from the combustion chamber exhaust through a turbine nozzle and thereafter through one or more turbine stages.
In many previously known turbine engines, the nozzle passageway is generally annular in shape having in its outer end open to the combustion chamber so that the gas stream through the nozzle passageway is directed radially inwardly. In addition, many of the previously known turbine engines include nozzle vanes extending across the nozzle passageway to aerodynamically control and shape the flow of the gas stream from the combustion chamber and to the turbine stages.
Many turbine engine applications require that the turbine engine be operated over a broad range of operating conditions. These different operating conditions have different gas stream flow requirements for maximum engine efficiency. Moreover, it is desirable to maintain high turbine engine efficiency at all engine operating conditions in order to minimize surge, cavitation and other engine instabilities while maximizing fuel economy.
One previously known method of broadening the flow capacity characteristics in the nozzle passageway is to use variable geometry engine components. One previously known method of varying the geometry of the turbine nozzle has been to pivot the nozzle vanes to the support housing and then the angle or pitch of the nozzle vanes.
The previously known pivoted nozzle vanes, however, have not proven wholly satisfactory in use. One disadvantage of this method results from the leakage losses from the nozzle passageway and around the pivoted nozzle vanes and into the support housing. These leakage losses are further amplified due to the large openings in the nozzle passageway walls which are required to compensate for thermal distortion and relative thermal expansion between the nozzle walls and the nozzle vanes.
A still further disadvantage of the previously known pivoted nozzle vanes is that it is difficult to accurately pivot all of the nozzle vanes to the same angle due to mechanical backlash and mechanical play. Unwanted and undesired turbulences result when the nozzle vanes are positioned at different angles.